54 
SPERMATOGENESIS OE NORMAE 
periments upon butterflies, shows that young hybrids at first 
resemble the female species, but with each succeeding meta¬ 
morphosis diverge more and more toward the. male species, 
until the hybrid comes to its final degree of intermediacy. 
The fact that denucleated fragments of eggs which have 
been fertilized by the sperm of another species give rise to off¬ 
spring which resemble the paternal species does not indicate 
necessarily that the conception under discussion is untenable. 
For example, BoverF in fertilizing a denucleated egg of one 
species of sea urchin with the nucleus of another species notes 
that the resulting animal when completely developed, resembles 
the latter species. This is just what one would under the cir¬ 
cumstances anticipate. We should expect the cytoplasm of 
the egg to determine none but the first general stages. Inas¬ 
much as there is chromatin present from one form only, the 
paternal, the individual finally produced would necessarily re¬ 
semble that form exclusively. 
The above statements are offered only in the form of sug¬ 
gestions. For a hypothesis to bear any probability of truth 
it must harmonize with existing facts, and there is none who 
will deny that existing facts in regard to heredity are far too 
few to admit of a dogmatic statement of any theory. Most 
suggestions are valuable, at present, only as they stimulate to 
the acquisition of more facts. 
SUMMARY. 
The points of special interest in the spermatogenesis of 
hybrid pigeons are as follows: 
1. The general plan of spermatogenesis is not essentially 
different from that of normal pigeons. 
2. From forms not too distantly related, fertile hybrids are 
easily obtained. 
3. Infertile hybrids, resulting from the crossing of very 
distinct species, are more difficult to secure. Females are rare. 
4. All hybrid pigeons exhibit multipolar spindles and 
1. Boveri, Th: Ueber die Befruchtungs-iind Entwlcklungs-fohigkeit kern- 
loser Seeigel-Eier.—Arch. Entwm. II, 1895. 
